ASA 5520 failover interfaces

I want to set up Active/Standby stateful failover. I only have 4 interfaces and 1 mgmt port. I have a outside, inside, and DMZ port configured. I want to use the last port for the stateful information and the MGMT port for the failover information. Is this the best (recommended) way to do this? Is there another way that would be better, possibly using the gig port for failover and stateful information?

Personally I would use your last gig port to do both failover and pass state information. The main thing is that the state link is a least the same speed as your fasted interface that you need to replicate. This is how I normally setup my customers firewalls.

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Personally I would use your last gig port to do both failover and pass state information. The main thing is that the state link is a least the same speed as your fasted interface that you need to replicate. This is how I normally setup my customers firewalls.

I would like to use my MGMT port for my management network, but I have never used the same cable for both failover functions. I know the gig port will not even get close to getting saturated. Is that the main concern and why Cisco recomends not doing that? Have you seen it cause issues?

It is recommended to have a dedicated interface for failover because the information is sent in clear text, and for performance reasons. It is ok though to share the 2 failover roles on one interface. The reason they recommend that the state link be the same speed as the fastest interface that you are replicating is so you won't miss anything in the event of a failover. If it is a very high use firewall, the connections need to be replicated as fast as they are happening on the other interfaces, so if something did casue a failover the connections will be there and ready to go on the standby device.